The present invention relates to a method for operating an internal combustion engine, in particular for a motor vehicle, in which the power output by the internal combustion engine is controlled and/or regulated as a function of performance quantities of the internal combustion engine and, in particular, as a function of a driver request. The present invention also concerns an internal combustion engine, in particular for a motor vehicle, having a control unit for controlling and/or regulating the power output by the internal combustion engine as a function of performance quantities of the internal combustion engine and, in particular, as a function of a driver request.
A method and an internal combustion engine of this type are known, for example, from German Patent Application 1 96 09 242. According to this publication, the performance quantities of the internal combustion engine are determined with the help of a multiplicity of sensors and supplied to an electronic control unit. The latter processes the performance quantities and activates a multiplicity of actuators, such as the injection valves and spark plugs of the internal combustion engine, as a function of these performance quantities. The power output by the internal combustion engine is controlled and/or regulated in this manner to the value desired, in particular, by the driver.
It is possible for sensors, in particular, to demonstrate measuring errors, for example due to aging phenomena. The consequence of this is that the entire control and/or regulation action of the internal combustion engine becomes susceptible to errors over time and no longer corresponds to the value desired by the driver.
For example, if an air-flow meter provided in the intake manifold of the internal combustion engine generates an incorrect output signal, this can lead to an excessive amount of fuel being injected into the combustion chamber of the internal combustion engine. This causes the internal combustion engine to generate a power that is much higher than the power desired by the driver.
In the above-mentioned German patent application, a monitoring system is provided that is used to continuously compare the power actually output by the internal combustion engine to a permissible power. The permissible power is detected, for example, on the basis of the accelerator position, i.e., on the basis of the power desired by the driver. If the actual power of the internal,combustion engine exceeds this detected permissible power, a sensor error is concluded. Appropriate action can thus be taken, in particular to correct the error.
It is known that, due to tolerances, different sensors of the same type frequently generate different output signals under the same conditions. In the monitoring system described according to German Patent Application 1 96 09 242, these tolerances of the input sensors must additionally be taken into account when detecting the actual and permissible power. As a result, the monitoring system detects only a major sensor error as being impermissible.
The object of the present invention is to provide a method for operating an internal combustion engine in which even minor sensor errors are detected early on.
This object is achieved according to the present invention with a method of the type mentioned in the preamble and an internal combustion engine of the type mentioned in the preamble in that a permissible variation in output power over a predetermined period of time and an actual variation in output power over a corresponding predetermined period of time are determined and compared to one another.
Thus, instead of monitoring the actual and permissible power of the internal combustion engine as absolute quantities, the method according to the present invention uses the variations in these absolute quantities, i.e., relative quantities, for monitoring purposes. According to the present invention, therefore, the variations in the actual and permissible powers, respectively, of the internal combustion engine are determined over a certain predetermined period of time. These variations, i.e., the relative quantities, are then compared to each other and, as a function of this comparison, action is taken as needed to correct the error.
In sensors of the same type, the tolerances of the individual sensors have an influence only on their absolute output signals. As previously mentioned in the preamble, these absolute output signals can therefore also vary among different sensors of the same type under the same conditions. However, it can be assumed that the variations in output signals, i.e., their relative quantities, remain essentially more or less the same in all sensors of the same type. In particular, these relative quantities remain more or less the same over a predetermined, preferably relatively short, period of time.
In other words, this means that the output signals of different sensors within the same sensor type vary in more or less the same way under the same conditions and over the same period of time. The sensor tolerances are therefore no longer a factor when using the relative quantities, i.e., when comparing the variations in the actual and permissible power of the internal combustion engine over the same predetermined period of time.
This means that the sensor tolerances no longer have to be taken into account, and thus smaller, in particular abrupt, sensor errors can even be detected. In particular, it is possible according to the present invention to detect the relative quantities, i.e., the actual and permissible variations in power output by the internal combustion engine, much more accurately without considering the tolerances than was previously possible with the absolute quantities of the actual and permissible power. This results in the above-mentioned advantage that even smaller variations, and thus smaller sensor errors, can be detected and indicated.
In advantageous embodiments of the present invention, the permissible variation in output power over the predetermined period of time is determined as a function of the speed of the internal combustion engine or the driver request, in particular as a function of the variation in the position of an accelerator. These actions have proved to be particularly simple and yet accurate means for calculating the permissible variation in the power output by the internal combustion engine.
In a further advantageous embodiment of the present invention, the actual variation in output power over the predetermined period of time is determined as a function of the oxygen content of the emitted exhaust gas and/or as a function of the intake air flow. These actions have proved to be particularly simple and yet accurate means for calculating the actual variation in the power output by the internal combustion engine.
It is particularly suitable if an error signal is generated if the actual variation in output power over the predetermined period of time is greater than the permissible variation in output power over the same predetermined period of time. This makes it possible to switch the internal combustion engine to an emergency mode, if necessary, or to alert the driver to the error and/or to take, some other action to correct the error.
In one advantageous :embodiment of the present invention, the performance quantities acting upon the internal combustion engine are converted: to torques, in particular to a permissible and an actual variation in a torque output by the internal combustion engine. Especially in the case of torque-driven internal combustion engines, and particularly in the case of lean-mix engines or engines with direct fuel injection, this has proven to be an especially effective means of monitoring the sensors.
It is especially important to implement the method according to the present invention in the form of an electric storage medium that is provided for a control unit of an internal combustion engine, in particular for a motor vehicle. On the electric storage medium is stored a program that can run on an arithmetic unit, in particular on a microprocessor, and is suitable for carrying out the method according to the present invention. In this case, therefore, the present invention is implemented by a program stored on the electric storage medium so that this storage medium provided with the program is equally representative of the present invention as the method which it is suitable to carry out.
Further features, applications, and advantages of the present invention can be derived from the following description of embodiments of the present invention, which are illustrated in the drawing. All described or illustrated features form the object of the present invention, either by themselves or in any combination, regardless of their combination in the patent claims or their references as well as independently of their formulation and depiction in the description and in the drawing, respectively.